Pocketed electrode plate for use in lithium ion secondary battery, its manufacturing method and lithium ion secondary battery using the same

ABSTRACT

A pocketed electrode plate for use in a ultra-slim lithium ion secondary battery, its manufacturing method and a lithium ion secondary battery using the same. The pocketed electrode plate comprises an electrode plate which has a coating layer of an electrode active material and a non-coated projection portion. The electrode active material can reversibly insert and extract lithium ions. The electrode plates further includes separating membranes which cover both sides of the electrode plate while exposing only the non-coated projection portion, and an insulating polymer having an adhesive component on both surfaces thereof. The insulating polymer film is placed adjacent to edges of the electrode plate but does not cover any portion of the electrode surface. The insulating polymer film is thermally bonded onto two separating membranes. A plurality of pocketed electrode plates may be produced by using a pressing roll.

TECHNICAL FIELD

The present invention relates to a lithium ion secondary battery, andespecially to a pocketed electrode plate for use in a lithium ionsecondary battery, its manufacturing method and the lithium ionsecondary battery using the same.

The present invention is to revolutionarily improve the productivity andenergy density of a slim lithium ion secondary battery with a thicknessof 5 mm or less.

BACKGROUND ART

To meet the growing and diversifying needs of markets for portableelectronic products such as mobile phones, camcorders and notebookcomputers, the demand for a rechargeable battery as a portable powersupply is also increasing. As these portable electronic products becomesmaller and lighter, while providing better performance andmulti-functional features, the requirement on the energy storage densityof a secondary battery is increasing very rapidly. Years of researchhave yielded the current lithium ion secondary battery that adopts apair of electrochemically active materials, typically lithium transitionmetal oxide for the cathode and carboneous material for the anode, whichallows lithium ion to be inserted into and extracted from the hoststructure of the material reversibly. The lithium ion secondary batteryhas higher energy density per unit volume as well as per unit weight andincreased charge and discharge lifetime compared to the existing aqueoussolution type secondary batteries such as Ni—Cd and Ni—MH batteries, andis rapidly replacing existing batteries for portable electronicproducts. However, the rapid development and diversification of portableelectronic products require batteries with higher energy density andmore flexible form factors, thus pushing the limit of the currentlithium ion secondary battery technology. In particular, the trend tomanufacture slim and small electronic products increases demands forultra-slim prismatic lithium ion secondary batteries however theadoption of current manufacturing methods for cylindrical or prismaticlithium ion batteries causes drastic lowering of energy density pervolume in manufacturing slim prismatic batteries. Therefore, when a slimprismatic battery with a thickness less than 5 mm is used for highperformance portable electronic products such as mobile phones,camcorders and notebook computers, it is difficult to maintainsufficient run time. Therefore, it is considered that the development ofa slim prismatic lithium ion secondary battery with higher energydensity per unit volume is essential in developing small, light and slimportable electronic products.

FIG. 1 is a schematic diagram of a manufacturing process of a prismaticlithium ion secondary battery described in a prior art. The anode andcathode of a prismatic lithium ion secondary battery is integrated intoone by the so-called winding method in which an anode and a cathode arerolled with a separator in-between them, and the integrated electrode iscalled a jelly roll. FIG. 1 shows that a lithium ion secondary batteryis manufactured by inserting the jelly roll 102 into a prismatic can 104followed by sealing the top with a cap 106 by laser welding. The anodeand the cathode are manufactured by covering a mixture of a polymerbinder, conductive powder and active material for each electrode ontocopper and aluminum thin plates, respectively. Usually, a non-coveredportion remains for the attachment of an electrode tab. An electrode tabmade of nickel and aluminum is attached to each non-covered portion ofan anode and a cathode respectively, and the two electrodes areconnected to external terminals through the tabs. One of the electrodetabs attached to the non-covered portion is bound to either a bottom ora side of a can 104 when the jelly roll 102 is inserted into a can 104,and the other tab is bound to a cap 106. The benefit of themanufacturing method and the structure is that the whole electrodesurface can be homogeneously utilized when a battery is charged ordischarged because the cathode and the anode are physically anduniformly attached to each other by the tension applied to a separatorin winding and they are also physically pressed to a wall of the can104. Therefore, the battery thusly made has superior performance andmaintains the high performance in the long term charging and dischargingcycle. An additional benefit of a wall of a metallic can 104 with highmechanical strength is that it can contribute greatly to the increase inenergy density per unit volume of a final battery because the jelly roll102 can be filled strongly inside a can 104 by physical pressing and thechange in thickness by swelling resulting from internal stress can beminimized. Furthermore, the complete fusion of the battery can 104 andthe cap 106 separates the battery inside from the outside and the dangerof a leak of battery internal material or infiltration of externalimpurities can be prevented.

However, the energy density of a slim prismatic lithium ion secondarybattery with thickness below 5 mm manufactured using the same electrodeunder the aforementioned assembly method will be lowered more than aconventional cylindrical battery by around 30% as long as theconstituent material is the same. The energy density will be decreasedeven further when the thickness is decreased. Furthermore, when thethickness is decreased most of the manufacturing processes such as jellyroll and electrolyte filling, insulation, separation of electrodeterminal and fusion using laser will be more difficult and results inthe lowering of yield and increase in manufacturing cost. The reasonsfor the decrease in energy density are summarized as below.

In first, the can for a prismatic battery in prior arts is usuallymanufactured by low temperature deep drawing, and the thickness of thecan is about 0.4 mm when it is made of aluminum and is 0.3 mm when it ismade of steel. The thickness of the packaging material of a cylindricalbattery is about 0.2 mm which is half or two thirds of that of analuminum or steel can. The volume or weight fraction of the thickpackaging material becomes bigger as the battery gets thinner especiallyfor a battery with thickness of 5 mm or less, and the use of aconventional can becomes a great limit in the manufacturing of a slimprismatic battery with high energy density.

In second, the shape of a jelly roll made by winding is not flat but israther elliptical and can not be inserted inside a prismatic batterytightly, and results in a dead space. The loss of energy density of abattery is determined by the volume fraction of unused internal space tothe whole internal space, and the loss of energy density for a slimprismatic battery with relatively small internal space will be severe.When the same electrodes are used, the energy density of a prismaticbattery with thickness below 4 mm is usually 30% lower than that withthickness around 10 mm.

In third, in the winding process for a prismatic battery, an electrodehas to be wound flatly unlike a cylindrical battery, which results inthe folding of an electrode due to decreased radius of curvature at theends of the jelly roll. In order to prevent damages on the electrode inthis process, the thickness of an electrode has to be decreased or theamount of non-active binder to enhance flexibility and adhesion has tobe increased. When several slim electrodes are wound more separatingmembranes and current collectors has to be incorporated into a battery,and the energy capacity of a battery decreases due to increased ratio ofnon-active material to active material. On the contrary, when the amountof non-active binder increases, the energy density of a batterydecreases as the amount of the non-active binder increases compared toactive electrode material.

The thinner the thickness of a prismatic battery is, the worse theproblem gets, and it becomes very serious in a prismatic battery withthickness below 5 mm. So, a conventional assembly method of a prismaticbattery can not satisfy the demand for ultra slim portable electronicproducts.

The decrease of energy density resulting from a jelly roll can beprevented by alternately stacking the existing slim separating membraneand electrodes. However, since the separating membrane is very flexible,alternate stacking of electrodes and separating membranes in a piece isvery difficult even in a manual process, and its application is close toimpossible considering productivity and yield. Furthermore, according tothe method of prior arts the matching of the edge of a cathode to theedge of an anode is difficult and the prevention of short-circuiting ofa cathode and an anode by a separating membrane is very difficult.

Therefore, in order to prevent the problem, a method of assembling astacked body comprising a cathode, an anode and a separating membrane isproposed by providing adhesion between the electrodes and a separatingmembrane. The adhesion is achieved by pressing polymeric electrolyte(that performs a dual role as a separating membrane and ion conductingelectrolyte) onto the surface of the electrode by heat and pressure orby covering the adhesive component at the contact surface between theelectrode and the separating membrane.

In U.S. Pat. Nos. 5,296,318 and 5,478,668, a battery maintainingadhesion without external pressure is proposed by applying ionconductive gel polymer onto an anode, a cathode and a separatingmembrane followed by heat lamination. This type of a battery is called alithium ion polymer battery or simply a polymer battery. This batteryemploys low ion conductive gel type polymer electrolyte as an ionconductor of an electrode and a separating membrane, so it showsinsufficient charging discharging speed and a decreased performance atlow temperature compared to the lithium ion battery. In addition, excessnon-active polymer is used for the electrode of a lithium ion polymerbattery even though there are variations in chemical composition, andthe thickness of a separating membrane has to be increased due to lowmechanical strength of an ion conductive separating membrane. Therefore,this type of a battery can not basically excel the prismatic lithium ionbattery in energy density per unit volume.

On the other hand, in order to fully exercise benefits of the existinglithium ion battery, U.S. Pat. No. 5,437,692 U.S. Pat. No. 5,512,389U.S. Pat. No. 5,741,609 and WO 9948162 disclose methods increasingadhesion between the two electrodes and a separating membrane by placinga thin adhesion layer between a separating membrane and an anode, and aseparating membrane and a cathode without employing polymer gelelectrolyte. In this structure, increased energy density can be obtainedand a stable battery performance is expected because the decrease ofionic conductivity is lowered compared to the gel type polymerelectrolyte and also the amounts of non-active polymer gel can begreatly decreased. However, in this technology discharging performancecan be decreased compared to the existing lithium ion battery due to acovering of conductivity decreasing adhesive material on the wholeactive electrode surface.

Therefore, in order to solve the problem, U.S. Pat. No. 5,981,107discloses a method of covering an adhesive component on the part ofinterface of an electrode and a separating membrane, and additionalformation of a convex and concave surface to increase moist containingcapacity of electrolyte. Furthermore, WO 0004601 discloses a method ofsticking an electrode to a separating membrane by forming a hole at thepart of an anode and a cathode followed by filling the hole withadhesive polymer. However, the process of forming an adhesive part isdifficult in this method. Especially, the U.S. Pat. No. 5,981,107 has aproblem of performance difference of a battery between the part coveredwith adhesive polymer and the non-covered part, and the method accordingto WO 0004601 has a difficulty of precise aligning of holes formed in ananode and a cathode.

Furthermore, in the aforementioned stacked body, there is an adhesionbetween an electrode and an electrolyte layer without pressure appliedby a packaging material, and a method in which a slim prismatic lithiumion secondary battery is manufactured by sealing a battery with analuminum laminate packaging material which is thinner and lighter thanexisting metal packaging material is proposed. The aluminum laminatepackaging material comprises a polymer layer capable of heat laminationsealing, a layer of material which is rarely penetrable by externalimpurities, and an insulating cover. Such packaging material has anadvantage that it is thinner and lighter than existing metal packagingmaterial. Accordingly, if it is used as a substitute for the metalpackaging material, the weight of a battery can be decreased and energydensity per unit thickness can be increased because the metal packagingmaterial contributes significantly to the thickness and weight of a slimbattery.

In addition, since the packaging material is electrically insulating, itis easy to insert multi-layer electrode stack or jelly roll without thedanger of short-circuiting. However, the mechanical strength of thepackaging material is low in spite of the merits of thin and lightcharacteristics, and there can be problems resulting from mechanicalweakness of a stacked packaging material even though adhesion between anelectrode and a separating membrane can be managed by any of theaforementioned method. Especially, the following three problems can befatal in the manufacturing and the use of a battery.

In first, a battery is sealed by heat lamination of innermost polymerlayer of aluminum laminated packaging material, and its sealing strengthis lower than that of laser sealing applied to existing prismaticbatteries. Especially, the sealing of a portion where an electrode tabis projected through packaging material is determined by the adhesionbetween a polymer layer and a metal layer, and there is always a gap atthe edge of the metal tab. Accordingly, the portion is prone to failuredue to leakage of electrolyte. Even in the middle of normal use, thesealing part comprising the metal tab and polymer cover can be easilycracked due to internal pressure increase resulting from expansion of anelectrode and gas generation, and there is a danger of leakage ofelectrolyte or introduction of external impurities such as moisture. Theproblem gets worse when gas is continuously generated due to impuritiesemanated from the electrode and electrode active material and impuritiesintroduced in each battery assembly step. So the introduction ofimpurities should be controlled strictly in each battery-manufacturingstep but it will also increase process cost. The danger of a leak due tocracks in adhesion layer is severe when the possibility of gasgeneration due to side reactions in a battery increases and the adhesionat the adhesion layer gets loosened which is observed at hightemperature. When there is a leak, it will be fatal to batteryperformance and it may contaminate and decrease the life span of theelectronic circuit of an expensive electronic product in which thebattery is placed.

In second, the existing prismatic battery employs a metallic can withenough mechanical strength and there is no severe increase in thicknessdue to internal pressure increase, but the aluminum laminate packagingmaterial can not bear internal pressure and the thickness of a batterymay increase. The increase of the thickness will change the appearanceof a battery pack, make it impossible to be normally placed in a batterypack, and bring on discontent in appearance. This problem is worsenedwhen the surface area of a battery is increased to enhance batterycapacity, which makes it difficult to manufacture a high capacitybattery with thickness below 5 mm.

In third, the weak mechanical strength of an aluminum laminate packagingmaterial lowers reliability and stability of a battery. A battery isused from at least 6 months to several years and requires superiordurability in a wide temperature range as well as under diversemechanical shocks. The existing prismatic battery adopts a metal can fora packaging material and the danger of damages due to external pressure,or local changes due to sharp ends such as a nail is not great but thealuminum packaging material has significantly decreased thickness andstrength compared to the existing metal packaging material and issusceptible to damages by external shock or fire. The stability issue iscritical to a high capacity battery used for a portable computer or to abattery used without an external plastic housing to make a slim batterypack.

The above review shows many limitations in manufacturing a durable,stable and slim battery with high energy density and easy manufacturingsteps. In summary, the existing prismatic lithium ion battery hasproblems resulting from a large portion of internal space that is notused due to a jelly roll type electrode structure, and energy density isdecreased greatly according to the decrease of total battery thicknessdue to a technical limit in decreasing thickness of a metal packagingmaterial manufactured by low temperature deep drawing. On the otherhand, a lithium ion polymer battery assembled by sealing a stackedelectrode body with an aluminum laminate packaging material hasdecreased dead space resulting from a jelly roll, but the energy densityis decreased and the battery performance is lowered because an excesspolymer binder is used for a sealing between electrodes or an adhesivelayer is coated on the interfacial surface of the electrode and theelectrolyte. Furthermore, the aluminum laminate packaging material hasproblems in durability and safety due to mechanical weakness andinsufficient adhesion at adhesive surface comprising a polymer cover anda metal tab.

DISCLOSURE OF THE INVENTION

One object of the present invention is to provide a pocketed electrodeplate which can prevent formation of wrinkles at separating membranes ofa pocketed electrode plate.

Another object of the present invention is to provide a lithium ionsecondary battery with high energy density using the pocketed electrodeplate.

A further object of the present invention is to provide a manufacturingmethod of a pocketed electrode plate suitable for mass production of alithium ion secondary battery.

In order to achieve the above objects, the present invention provides apocketed electrode plate for use in a lithium ion secondary batterymanufactured by an electrode-stacking manner, the pocketed electrodeplate comprising:

an electrode plate which has a coating layer of an electrode activematerial and a non-coated projection portion, the electrode activematerial being capable of reversibly inserting and extracting lithiumions;

separating membranes which cover both sides of the electrode plate whileexposing only the non-coated projection portion; and

an insulating polymer film which contains an adhesive component and isplaced between the separating membranes at least on the portion of theexternal edge of the electrode plate in order to bond and fix theseparating membranes.

In order to achieve the above objects, the present invention provides alithium ion secondary battery having stacked electrodes, the batterycomprising:

(a) a plurality of pocketed cathode plates, each cathode electrode platecomprising,

(a-1) an electrode plate which has a coating layer of an electrodeactive material and a non-coated projection portion, the electrodeactive material being capable of reversibly inserting and extractinglithium ions;

(a-2) separating membranes which cover both sides of the electrode platewhile exposing only the non-coated projection portion; and

(a-3) an insulating polymer film which contains an adhesive componentand is placed between the separating membranes at least on the portionof the external edge of the electrode plate in order to attach and fixthe separating membranes; and

(b) a plurality of anode plates, each anode plate containing a materialcapable of reversibly inserting and extracting lithium ions; wherein thecathode and anode plates are alternately stacked.

Preferably, the size of the pocketed cathode plate is no smaller thanthat of the anode plate, and the area of the anode plate is larger thanthat of the coating layer of the cathode plate.

In order to achieve the above objects, the present invention provides amethod of manufacturing pocketed electrode plates for use in a lithiumion secondary battery manufactured by an electrode-stacking manner, themethod comprising the steps of:

(a) providing a plurality of electrode plates having the same shape,each of which has a coating layer of an electrode active material and anon-coated projection portion, the electrode active material beingcapable of reversibly inserting and extracting lithium ions;

(b) providing a tape-shaped insulating polymer film with both sidescovered with an adhesive component;

(c) blanking parts of the polymer film so that the polymer film may haveempty regions where the electrode plates are aligned and contained to aspecified spacing;

(d) aligning the electrode plates within the empty regions to aspecified spacing;

(f) locating tape-shaped separating membranes on both sides of thepolymer film with electrode plates contained therein in order to coverthe electrode plates while exposing only the non-coated projectionportions of the electrode plates;

(g) passing the polymer film covered with the separating membranesthrough a pressing roll in a heated state; and

(h) stamping out the pressed polymer film to form a plurality ofpocketed electrode plates;

wherein each pocketed electrode plate is stacked in the order of aseparating membrane/an electrode plate/a separating membrane, and

wherein the separating membranes are bonded by the insulating polymerfilm at least on the portion of the external edge of the electrodeplate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a manufacturing process of a prismaticlithium ion secondary battery described in a prior art;

FIGS. 2A to 2G are diagrams of a manufacturing process of a pocketedelectrode plate according to one example of the present invention; and

FIG. 3 is a diagram comparing the size of a pocketed electrode plate andan anode plate used in one example of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, preferred embodiments of the present invention will beexplained with reference to the attached drawings and the pocketedelectrode plate and its manufacturing method are explained together butthe pocketed electrode plate is limited to the cathode plate in theexample.

FIGS. 2A to 2G are diagrams of a manufacturing process of a pocketedelectrode plate according to one example of the present invention.

FIG. 2A is a diagram illustrating one example of insulating polymer filmto manufacture a pocketed electrode plate according to the presentinvention. In FIG. 2A, there are multiple longitudinal perforated spaces210 on a continuous roll of polymer film covered with an adhesivecomponent on both sides. The perforated space 210 are separated at anequal distance with the same shape, and each perforated space 210 areformed bigger than the cathode plate to position the cathode plates at adistance as described below. In manufacturing a pocketed electrode plateof the present invention, the diverse shape of perforated space of aninsulating polymer film can be selected only if the cathode plates arecontained within the empty regions of the insulating polymer film to aspecified spacing and the polymer film surrounds at least edge portionof each cathode plate. Therefore, if the cathode plate is rectangular inshape with a non-coated projection portion, then the desirable shape ofa perforated space of polymer film is such that it surrounds at leasttwo sides of the cathode plate.

FIG. 2B is another example of an insulating polymer film to manufacturea pocketed electrode plate according to the present invention. FIG. 2Bshows that there is a perforated space 210′ with its shape changingperiodically on the continuous roll of polymer film 200 with an adhesivecomponent on both sides.

Preferably, the insulating polymer film is selected from a groupconsisting of polyolefin film, polyester film, polystyrene film,polyimide film, polyamide film, fluorocarbon resin film, ABS film,polyacrylic film, acetal film, and polycarbonate film.

Furthermore, the adhesive component covered on both sides of theinsulating polymer film is preferably selected from a high temperaturefused adhesive group consisting of ethylene vinyl acetate, ethyleneethyl acetate, ethylene acrylic acid type compound, ionomer typecompound, polyethylene, polyvinylacetate, and polyvinylbutyral.

FIG. 2C is a diagram showing the step of locating a cathode plate and aseparating membrane inside a perforated space of insulating polymer film200 of FIG. 2A. FIG. 2C shows that the cathode plate comprising acoating layer of lithium transition metal oxide, the cathode activematerial, and a non-coated projection portion are located with aspecified spacing in each perforated space. The size of a cathode plateor a perforated space is controlled to keep the spacing around theprojection portion of the cathode plate bigger than the spacing in otherportions. Thereafter, separating membranes (not drawn) with width of dis placed on both sides of polymer film 200 which is located with thecathode plate 220, but only the non-coated projection portion on thecathode plates 220 are exposed while other portion of the cathode platesare covered. In FIG. 2C, the space occupied by separating membranes isspacing in-between one-dot chain line. In FIG. 2C, the space inside adotted line S is a cutting line to obtain each pocketed electrode plateafter pressurizing and adhering processes described below. According tothe procedure described above, a roll of resulting material laminated inthe order of lower separating membrane/insulating polymer film coveredwith adhesive component and cathode plate located at the perforatedspace of the polymer film/upper separating membrane can be obtained.

FIG. 2D is a diagram showing the step of locating a cathode plate and aseparating membrane inside a perforated space of the insulating polymerfilm 200 of FIG. 2B. FIG. 2D shows that separating membranes (not drawn)with width of d′ is located on both sides of the polymer film 200 whichis located with the cathode plate 200. The size of the cathode plates220 or that of perforated space is determined so that the non-coatedprojection portion of the cathode plate is projected outside the polymerfilm 200. In FIG. 2D, the separating membrane has the same width withthe polymer film and is placed along the polymer film. In FIG. 2C, thespace inside a dotted line S is also a cutting line to obtain eachpocketed electrode plate after pressurizing and adhering processesdescribed below.

FIG. 2E is a diagram showing a pressurizing process of a resultingmaterial of FIG. 2C. In FIG. 2E, the resulting material comprising aninsulating polymer film 200 covered with separating membrane230/adhesive component and cathode plate 220/separating membrane 230located at the perforated space is heated and fused in the shape of acontinuous scroll by a pressure roll 250. In FIG. 2E, the resultingmaterial of FIG. 2C is represented by a longitudinal cross section. Bythe pressurized fusing a strong adhesion is achieved wherever theinsulating polymer film is but there is no adhesion or deformation wherethe cathode plate 220 is.

Desirable separating membrane used by the above example is a porouspolymer film made of a polyolefin material with a porous ratio of 25-60%and a width of 10-30 micron. Furthermore, the desirable heated fusingtemperature for polyethylene is below 120° C. and that of polypropyleneis below 150° C.

FIG. 2F is a diagram showing a pocketed electrode plate manufactured byperforating the pressurized resulting material according to theexplanation of FIG. 2E along the dotted line of FIG. 2C. In FIG. 2F, theadhesive portion of the cathode plate 220 and the insulating polymerfilm 200 is drawn perspectively to clarify the drawing. In FIG. 2F, theadhesive portion surrounds all the external edge of the cathode plate220, and only the non-coated projection portion of the cathode plate 220is exposed without being covered by the separating membrane 230.

If a pocketed electrode plate is manufactured using the resultingmaterial drawn in FIG. 2D, the adhesive portion will surround only theupper and lower external edges of the cathode plate.

If a pocketed electrode plate is manufactured by the method describedabove, a mass production of a pocketed electrode plate is possible.

FIG. 2G is a cross-sectional view along the A-A′ line of FIG. 2F. Asshown in FIG. 2G, the difference between the thickness of a stackedportion of separating membrane 230/cathode plate 220/separating membrane230 and that of separating membrane 230/insulating polymer film 200covered with an adhesive component/separating membrane 230 is smallerthan those in prior arts, and the generation of wrinkles in theseparating membrane of the pocketed electrode plate manufacturedaccording to the present invention is decreased.

FIG. 2C is a diagram comparing the size of the pocketed electrode plateand the anode.

When a lithium ion secondary battery is manufactured by an electrodeplate stacking method, it is desirable to keep the size of theperforated pocketed electrode plate equal to or bigger than that of theanode plate and the size of the anode plate bigger than that of thecathode active material covered area of the cathode plate in order toprevent edge mismatch of active plate of an anode and a cathode and tomaintain a smooth stacking alignment. Therefore, as shown in FIG. 3, ifboth the cathode plate and the anode plate are rectangular with anon-coated projection portion, it is desirable to follow the equation 1among the width of the cathode plate B, the width of a separatingmembrane for pocketing and the width of an anode plate C.A≧C≧B+A−B/2  [Equation 1]More desirably, if the pocketed electrode plate except for eachprojection portion and the edge anode are made to coincide, thecondition that all plates facing the cathode should be covered with ananode is automatically satisfied.

After aligning and stacking the pocketed electrode plates and the anodeplates, the non-coated projection portions of the anode plates are fusedto one another and the non-coated projection portions of the cathodeplates are fused to one another. Then, each of them is connected to ananode tab and a cathode tab, respectively. By sealing it inside a metalpackaging material, a lithium ion secondary battery is manufactured.

The performances of the lithium ion secondary battery manufacturedaccording to the present invention are summarized as below.

[Prismatic Battery with Thickness of 2.4 mm]

For a prismatic battery having curved corners manufactured withthickness of 2.4 mm, short diameter of 35 mm and long diameter of 62 mm,the reversible capacity is 620 mAh which is 440 Wh/liter when convertedto energy density per volume.

[Prismatic Battery with Thickness of 4.0 mm]

For a prismatic battery having curved corners manufactured withthickness of 4.0 mm, short diameter of 35 mm and long diameter of 62 mm,the reversible capacity is 1100 mAh which is 470 Wh/liter when convertedto energy density per volume.

The pocketed electrode plate manufactured according to the presentinvention has higher adhesive strength with decreased adhesion area and,therefore, the energy density of a finished lithium ion secondarybattery can be increased. Furthermore, the pocketed electrode plate canbe manufactured in a continuous roll process, and a mass production of alithium ion secondary battery is made easy. Herein above the inventionhas been described in reference to the preferred embodiments, butvarious other modifications and variations will be apparent to thoseskilled in the art without departing from the scope and spirit of thepresent invention. The pocketed electrode plate is limited to a cathodeplate in the example of the present invention, but it is understood thatan anode electrode plate can be used as a pocketed electrode plate asfar as the limitation condition on the active material covering area issatisfied.

1. A pocketed electrode plate for use in a lithium ion secondary batterymanufactured by an electrode-stacking manner, the pocketed electrodeplate comprising: an electrode plate which has a coating layer of anelectrode active material and a non-coated projection portion, theelectrode active material being capable of reversibly inserting andextracting lithium ions; separating membranes which cover both sides ofthe electrode plate while exposing only the non-coated projectionportion; and an insulating polymer film having an adhesive component onboth surfaces thereof, the insulating polymer film being placed adjacentto edges of the electrode plate but not covering any portion of thecoating layer of the electrode plate, wherein the insulating polymerfilm is sandwiched between the two separating membranes, and wherein theinterface between the insulating polymer film and separating membrane isbonded by a thermal fusion of the adhesive component on the bothsurfaces of the insulating polymer film, and wherein the separatingmembranes are in direct contact with the both sides of the electrodeplate.
 2. The pocketed electrode plate of claim 1, wherein theinsulating polymer film is selected from the group consisting ofpolyolefin film, polyester film, polystyrene film, polyimide film,polyamide film, fluorocarbon resin film, ABS film, polyacrylic film,acetal film, and polycarbonate film.
 3. The pocketed electrode plate ofclaim 2, wherein the adhesive component on the insulating polymer filmis comprised of a compound selected from the high temperature melt fusedadhesive group consisting of ethylene vinyl acetate, ethylene ethylacetate, ethylene acrylic acid, polyethylene, poly-vinyl-acetate, andpoly-vinyl-butyral.
 4. The pocketed electrode plate of claim 1, whereinthe electrode plate pocketed by the separating membranes is a cathodeplate.
 5. The pocketed electrode plate of claim 1, wherein theseparating membranes comprise a porous polymer film.
 6. The pocketedelectrode plate of claim 5, wherein the porous polymer film is made of apolyolefin material with a porous ratio of 25-60% and a width of 10-30microns.
 7. A lithium ion secondary battery having stacked electrodes,the battery comprising: (a) a plurality of pocketed cathode plates, eachcathode electrode comprising, (a-1) an electrode plate which has acoating layer of an electrode active material and a non-coatedprojection portion, the electrode active material being capable ofreversibly inserting and extracting lithium ions; (a-2) separatingmembranes which cover both sides of the electrode plate while exposingonly the non-coated projection portion; and (a-3) an insulating polymerfilm having an adhesive component on both surfaces thereof, theinsulating polymer film being placed adjacent to edges of the electrodeplate but not covering any portion of the coating layer of the electrodeplate, wherein the insulating polymer film is sandwiched between the twoseparating membranes, and wherein the interface between the insulatingpolymer film and separating membrane is bonded by a thermal fusion ofthe adhesive component on the both surfaces of the insulating polymerfilm; and (b) a plurality of anode plates, each anode plate containing amaterial capable of reversibly inserting and extracting lithium ions;wherein the separating membranes are in direct contact with the bothsides of the electrode plate.
 8. The lithium ion secondary battery ofclaim 7, wherein the size of the pocketed cathode plate is no smallerthan that of the anode plate, and wherein the area of the anode play islarger than that of the coating layer of the cathode plate.
 9. A methodof manufacturing pocketed electrode plates for use in a lithium ionsecondary battery manufactured by an electrode-stacking manner, themethod comprising: (a) providing a plurality of electrode plates havingthe same shape, each of which has a coating layer of an electrode activematerial and a non-coated projection portion, the electrode activematerial being capable of reversibly inserting and extracting lithiumions; (b) providing a tape-shaped insulating polymer film with bothsides covered with an adhesive component; (c) blanking parts of thepolymer film so that the polymer film may have empty regions where theelectrode plates are aligned and contained to a specified spacing; (d)aligning the electrode plates within the empty regions to a specifiedspacing; (f) locating tape-shaped separating membranes on both sides ofthe polymer film with electrode plates contained therein in order tocover the electrode plates while exposing only the non-coated projectionportions of the electrode plates; (g) passing the polymer film coveredwith the separating membranes through a pressing roll in a heated state;and (h) stamping out the pressed polymer film to form a plurality ofpocketed electrode plates; wherein each pocketed electrode plate isstacked in the order of a separating membrane/ an electrode plate/ aseparating membrane, and wherein the separating membranes are bonded bythe insulating polymer film at least on the portion of external edges ofthe electrode plate.
 10. The method of claim 9, wherein the electrodeplate pocketed with the separating membranes is a cathode plate and thesize of the stamped-out cathode plate is no smaller than that of ananode plate, and wherein the area of the anode plate is larger than thatof the coating layer of the cathode plate.
 11. The method of claim 9,wherein the insulating polymer film is selected from the groupconsisting of polyolefin film, polyester film, polystyrene film,polyimide film, polyamide film, fluorocarbon resin film, ABS film,polyacrylic film, acetal film, and polycarbonate film.
 12. The method ofclaim 11, wherein the adhesive component is selected from the hightemperature fused adhesive group consisting of ethylene vinyl acetate,ethylene ethyl acetate, ethylene acrylic acid, polyethylene,polyvinylacetate, and polyvinylbutyral.